The present invention relates to a video camera which displays a warning when a battery becomes near empty, and a warning method thereof.
Conventionally known as a power source of a video camera is, for example, a battery pack including a lithium ion battery, NiCd battery, nickel hydrogen battery, or the like as a secondary battery cell. The battery pack is constructed to be detachable from a battery attachment section provided in the video camera apparatus body.
Normally, in an electric apparatus such as a video camera using this battery pack as a power source, the battery end voltage is determined depending on the terminal voltage of the battery pack. Also, displaying of a warning prior to end of the battery is determined depending on the terminal voltage of the battery pack. The battery end voltage and the voltage for displaying a warning prior to end of battery are generally fixed.
Meanwhile, the discharge characteristic (defined by subtracting a discharge time from a between terminal voltage) of the battery pack differs depending on the type of the battery cell. Even one same cell may have different discharge characteristics, depending on the cell structure method. Therefore, if the battery end voltage Ve and the warning display voltage Vp prior to end of the battery are both fixed, there is a problem that the time from when a warning is displayed to when the battery actually ends greatly varies depending on the type of the battery pack. For example, suppose three cell structures, e.g., a one-stage cell structure in which two battery cells C1 and C2 are connected in series as shown in FIG. 1(A), a two-stage cell structure in which two stages each consisting of two battery cells C1 and C2 connected in series are connected in parallel as shown in FIG. 1(B), and a three-stage cell structure in which three stages each consisting of two battery cells C1 and C2 are connected in series are connected in parallel as shown in FIG. 1(C). Between these three cell structures, the times T1, T2, and T2 at which warnings prior to end are displayed are greatly different from each other as indicated by the relationships between the battery discharge characteristics F1, F2, and F3 and the warning display times T1, T2, and T3 in FIG. 2.
This problem means lowered reliability with respect to warning display near the battery end of the electric apparatus, and the influence therefrom increases as the consumption power of the apparatus decreases.
The present invention hence has an object of providing a video camera and a warning display method thereof which enable warning display with high reliability.